Introduction
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Phase I, hydrolysis, characterized by high concentrations of organic substances in the leachate, aerobic conditions in the landfill, and a high content of readily biodegradable organic materials in the waste. The final products of hydrolysis are monosaccharides, amino acids, long-chain organic acids, and glycerol, which are substrates for the acid phase;
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Phase II, acidic, also characterized by high levels of organic substances in the leachate, intensive production of short-chain organic acids, a decrease in pH (5.5–6.5), and methane production at a level that is not detectable;
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Phase III, unstable methane, characterized by increased pH, a decrease in redox potential to negative values, a decrease of volatile fatty acids concentrations and organic substances in leachate, a reduction in sulfates to sulfites, and intensive production of methane;
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Phase IV, methane stable, characterized by relatively constant, low concentrations of organic materials in the leachate, a growth of redox potential, a decrease of biogas production, and a methane content in biogas at a relatively constant, high level—around 60–70 %.
Materials and methods
Research material
Research area
Process operation
Results
Chemical properties and composition of waste
Parameters | MSW | ST |
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Waste properties | ||
Moisture content, % | 40.2 | 34.5 |
Volatile solid, % of dry matter | 58.5 | 52.2 |
Organic carbon, kg/kg of dry matter | 0.38 | 0.27 |
Composition of the waste (average percentage wet weight) | ||
Food and vegetable leftovers | 42.5 | 32.6 |
Paper and cardboard | 17.5 | 14.9 |
Glass | 9.8 | 12.5 |
Plastic | 13.5 | 17.7 |
Textile | 2.5 | 2.9 |
Packing material (miscellaneous composition) | 2.5 | 3.6 |
Wood | 0.1 | 0.1 |
Metal | 1.6 | 1.9 |
Mineral waste | 10.0 | 13.8 |
Overall | 100 | 100 |
Amount and composition of biogas and leachate
Reactor | MSW | ST | MSW | ST | ||||||
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Phase | I | II | III | IV | I | II | III | IV | I–IV | I–IV |
COD, g/dm3
| 34.6 | 29.2 | 16.3 | 1.6 | 43.3 | 45.9 | 23.5 | 1.3 | 18.7 | 16.9 |
VFA, g/dm3
| 9.6 | 10.72 | 8.7 | 1.1 | 13.4 | 16.1 | 10.4 | 0.3 | 7.9 | 6.2 |
pH | 4.8–6.4 | 4.7–5.3 | 4.6–6.5 | 6.2–6.8 | 5.3–6.0 | 5.3–5.8 | 5.3–7,0 | 6.8–7.4 | 4.6–6.8 | 5.3–7.4 |
CH4, % | 0 | 14.9 | 52.1 | 62.6 | 0 | 10.6 | 48.1 | 63.8 | 39.7 | 46.9 |
CH4 production, dm3/kg | 0 | 4.7 | 184.3 | 50.7 | 0 | 4.3 | 56.2 | 150.6 | 230.4 | 202.0 |
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Phase I: COD 25 %, VFA 28 %,
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Phase II: COD 36 %, VFA 33 %
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Phase III: COD 31 %, VFA 16 %,
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Phase IV: COD 19 %, VFA 72 %.
Discussion
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COD, TOC, BOD5, and VFA: 21, 18, 6, and 23 %,
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Total nitrogen and ammonium: 7 and 50 %.